Multi-chip module leadless package

ABSTRACT

A multi-chip module (MCM) package includes a leadframe including half-etched lead terminals including a full-thickness and half-etched portion, and second lead terminals including a thermal pad(s). A first die is attached by a dielectric die attach material to the half-etched lead terminals. The first die includes first bond pads coupled to first circuitry configured for receiving a control signal and for outputting a coded signal and a transmitter. The second die includes second bond pads coupled to second circuitry configured for a receiver with a gate driver. The second die is attached by a conductive die attach material to the thermal pad. Bond wires include die-to-die bond wires between a portion of the first and second bond pads. A high-voltage isolation device is between the transmitter and receiver. A mold compound encapsulates the first and the second die.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Provisional Application No.62/977,539, entitled “Architecture, circuit, and structure forinput-to-output and channel-to-channel isolation in a thermally-enhancedleadless package”, filed Feb. 17, 2020, which is herein incorporated byreference in its entirety.

FIELD

This Disclosure relates to multi-chip modules including a transmit (Tx)die and a receive (Rx) die having die-to-die bonding, also including ahigh-voltage (HV) isolator between the respective die.

BACKGROUND

Some packaged semiconductor devices comprise a multi-chip module (MCM)package which includes two or more IC die within the package. Electricalconnections between the respective IC die when laterally positioned ondie pads within a MCM generally include bond wires connecting to innerlocated bond pads on the respective IC die including die-to-die bondwires. One known MCM arrangement is a Small Outline Integrated Circuit(SOIC) package.

One MCM package arrangement known as a digital isolator comprises afirst IC die and a second IC die generally including communicationchannels including a Tx die and a Rx die, where some bond pads on therespective die are coupled together by bond wires, and at least one ofthe die includes at least one high voltage isolation (HV ISO) device,such as a HV capacitor, connected in series in the data channel path.This arrangement enables modulated data signals generated on the Tx dieto be passed to the Rx die, but blocks high voltage (e.g., 500 or 1,000volts during a surge) applied to the active circuitry on the Rx die whenin its application from reaching the active circuitry on the Tx die.

Some circuits, such as DC/DC telecom power modules, include what isreferred to as brick isolation, are configured with MCMs that involve aTx die configured for receiving a control signal (such as a pulse widthmodulation (PWM) signal received from a microcontroller unit (MCU)) andat least one Rx die including a receiver with a gate driver configuredfor driving gates of power transistors (e.g. insulated gate bipolartransistors (IGBTs) or metal oxide field-effect transistors (MOSFETs))to support two gate drive channels, or there is a first and a second Rxdie each supporting one channel. There is at least one HV ISO device,also called a digital isolator, such as HV ISO device comprising a HVcapacitor in the signal path between the Tx die and the Rx die for eachchannel. A DC/DC telecom brick module is an end application example thatincludes a digital isolator. The digital isolator employed in anisolated DC/DC telecom brick module is typically realized as an MCMpackage. In operation of the DC/DC telecom brick module, the transmittertransmits control signals across the digital isolator to the receiver.

Such DC/DC telecom brick modules generally include a spacing from the Txdie (as an input circuit) to the Rx die (as an output circuit), as wellas between the respective channels (such as between a first channel anda second channel) that are minimized to the extent possible to reducethe DC/DC telecom brick module's size but to still remain sufficient tomeet reliability considerations associated with high electric fields.Such DC/DC telecom brick modules are configured to operate with the Rxdie connected to a DC voltage input, where the HV ISO device protectsthe Tx die from high voltage transients that may occur on the DC voltageinput, and where the DC/DC telecom brick module is configured to operateat a high frequency and over a wide ambient temperature range.

SUMMARY

This Summary is provided to introduce a brief selection of disclosedconcepts in a simplified form that are further described below in theDetailed Description including the drawings provided. This Summary isnot intended to limit the claimed subject matter's scope.

Disclosed aspects recognize for MCM applications, such as for DC/DCtelecom brick modules including a Tx and signal coding die (referred toherein as a “Tx/signal coding die”) and a Rx and driver die (referred toherein as a “Rx/driver die”), having a HV ISO device in between, themaximum isolation requirement may be a 2.25 kV DC withstand voltage withat least 1.3 mm of creepage and clearance distance between the leadterminals (also referred to as pins) of the Tx/signal coding die. TheTx/signal coding die is generally on one side of the MCM package and theRx/driver die is on an opposite side of the MCM package. As theseapplications strive for higher power density, the DC/DC telecom brickmodule size needs to decrease.

A smallest dual (two channel)-isolated gate driver for the Rx/driver diemay be designed for high working voltages (e.g., >>48V) in a 5 mm×5 mmpackage with greater than a 3.5 kV DC withstand voltage between theinput and the output lead terminals and 3.5 mm of spacing between theinput and output terminals. The high working voltage and withstandvoltage need a large spacing between the lead terminals of the Tx/signalcoding die and the Rx/driver die, which leaves little or no room forexposed relatively large area “thermal pads”, also known as power pads,needed for cooling the Rx/driver die during its operation to enable itto operate at higher frequency and temperature, especially at relativelysmall package sizes.

Disclosed aspects provide a MCM leadless package (MCM package) include aTx/signal coding die and at least one Rx/driver die including somedie-to-die wire bonding, also including a HV isolator device in a signalpath between the Rx/driver die and the Tx/signal coding die. DisclosedMCM packages comprise a leadless leadframe having a plurality of leadterminals including at least one thermal pad for enabling a directthermal connection to a PCB which may be mounted below using a volumeunder the Rx/driver die to enable higher power dissipation. Also enabledis an increased external Tx/signal coding die to Rx/driver die creepagedistance for helping with the isolation requirement by placing theTx/signal coding die (that has a relatively low power dissipation) ontolead terminals that have half-etched distal portions referred to hereinas half-etched lead terminals that because of the half-etching have areduced externally exposed (from the mold compound) length.

Disclosed MCM packages comprise a leadframe comprising half-etched leadterminals including a full-thickness portion and half-etched portion,and a second lead terminal including a thermal pad(s). A first die isattached by a dielectric die attach material to the half-etched leadterminals. The first die includes first bond pads coupled to firstcircuitry configured for receiving a control signal and for outputting acoded signal and a transmitter. The second die includes second bond padscoupled to second circuitry configured for a receiver with a gatedriver. The second die is attached by a conductive die attach materialto the thermal pad. Bond wires include die-to-die bond wires between aportion of the first bond pads and the second bond pads. A high-voltageisolation device is between the transmitter and receiver. A moldcompound encapsulates the first die and the second die.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, wherein:

FIG. 1A is a top view depiction of a disclosed small outline no leads(SON) leadframe for a MCM package configured for receiving on an inputside a Tx/signal coding die, and receiving on an output side including afirst Rx/driver die and a second Rx/driver die, according to an exampleaspect.

FIG. 1B is a top view depiction of a disclosed MCM package shown in FIG.1A that now shows bond wire connections along with a Tx/signal codingdie and a first Rx/driver die and a second Rx/driver die on the leadterminals of the package.

FIG. 2 is a cross-sectional view of the MCM package shown in FIG. 1B.The Tx/signal coding die is now shown on half-etched lead terminals thatincludes a full-thickness portion and distal half-etched (or cantilever)portion. Half-etched lead terminals provide mechanical support for dieplacement and bonding, but the half-etched portion is not exposedexternally (covered by mold compound) to provide an increasedinput/output spacing of the lead terminals.

FIG. 3 shows example steps for a first assembly flow for forming adisclosed MCM package, according to example aspect.

FIG. 4 shows example steps for a second assembly flow for forming adisclosed MCM package, according to example aspect. The second assemblyflow differs from the first assembly flow by utilizing separate curingfor the B-stage die attach material and the epoxy material. Theadvantage of the separate curing is that each cure step can beseparately optimized for the die attach material selected, and moreoverthere is less time between placement of the first die and the curingstep which can improve the adhesion of the first die attach material.

FIG. 5 shows a disclosed MCM package as part of a DC/DC telecom brickpower module including a first and a second disclosed MCM package.

DETAILED DESCRIPTION

Example aspects are described with reference to the drawings, whereinlike reference numerals are used to designate similar or equivalentelements. Illustrated ordering of acts or events should not beconsidered as limiting, as some acts or events may occur in differentorder and/or concurrently with other acts or events. Furthermore, someillustrated acts or events may not be required to implement amethodology in accordance with this Disclosure.

Also, the terms “coupled to” or “couples with” (and the like) as usedherein without further qualification are intended to describe either anindirect or direct electrical connection. Thus, if a first device“couples” to a second device, that connection can be through a directelectrical connection where there are only parasitics in the pathway, orthrough an indirect electrical connection via intervening itemsincluding other devices and connections. For indirect coupling, theintervening item generally does not modify the information of a signalbut may adjust its current level, voltage level, and/or power level.

FIG. 1A is a top view depiction of a disclosed leadframe shown as a SONleadframe 110 for a MCM package including two channels configured forreceiving on an input side a Tx/signal coding die, and on an output sidea first R_(X)/driver die as well as second Rx/driver die, along withsome examples lead terminal spacings shown, according to an exampleaspect. The SON leadframe 110 may also be referred to as being a quadflat no lead (QFN) leadframe. The GND terminal is shown having achamfered corner for visual inspection systems to detect it as the pin 1corner of the device. The SON leadframe 110 has its pins shown numbered1 (ground (GND)) to 13 (VDDA).

Also provided is an example pinout along with some examples leadterminal spacings shown. On the input side, there are half-etched leadterminals shown as pins 1 to 7 collectively shown as 115 including aninput A (INA/pulse width modulation (PWM)) terminal for controlling thefirst Rx/driver die and for controlling the second Rx/driver die, suchas received from a microcontroller. Although the other input terminal inFIG. 1 a INB is shown being a no connect (NC) terminal, the INB terminalcan be used for receiving a second PWM signal so that the that firstRx/driver die and the second Rx/driver die are controlled by differentcontrol signals.

The half-etched lead terminals 115 also include first and second GNDterminals. There is also shown on the input side a VCC terminal shown asVCCI, an enable pin (EN), and a dead time (DT) pin. On the output sideshown as pins 8 to 13 there are output side terminals collectively shownas 125 that include for each channel a voltage drain power supply (VDD)terminal, shown as VDDA and VDDB, output (OUT) terminals shown as OUTAand OUTB, and a voltage source supply (V_(SS)) terminal for each channelshown as VSSA and VS SB. The VSSA and VSSB terminals can be seen tocomprise thermal pads. As used herein the term “thermal pad” is definedto be an exposed lead terminal that comprise a solid metal (generallybeing copper typically with an optional surface finish for enhancedsolderability or bond ability), comprising the same metal as theremainder of the leadframe.

The thermal pad has an area that is larger than the die that is placedthereon in both the X and Y dimension, so that the thermal pad fullyencompasses the area of the die from a layout perspective. Additionally,a thermal pad being larger in area as compared to the die that ismounted thereon allows for the use of a liquid epoxy to connect theR_(X/)driver die to the thermal pad. Conventional liquid epoxy materialscan be filled with metal particles, such as silver nanoparticles, whichprovides a substantially higher thermal conductivity as compared to apolymer epoxy material alone.

The SON leadframe 110 is shown having example outer (overall) dimensionsof 4 mm by 4 mm, with an example spacing between the distal end of theVSSA and VSSB terminals of the output side lead terminals 125 and thehalf-etched lead terminals 115 on the input side shown as being 1.6 mm.Also shown as a channel-to-channel spacing defined by a spacing betweenthe VSSA and the VSSB terminals being 1.2 mm. More generally, to supporta voltage difference that can be several hundreds of volts between theinput side and the output side of a disclosed MCM packaged device duringoperation during a spike or a transient, an external spacing between thehalf-etched lead terminals 115 and the VSSA and the VSSB terminals is atleast 1 mm and/or is least 30% of a length of an MCM package thatutilizes the leadframe 110. Having separate VSS terminals splits the GNDplane on the output side into two sections so that each channel has itsown ground reference. Ground plane splitting is helpful because incertain applications they are referenced to different voltage nodes.This ground plane splitting can be part of a >200V channel-channelspacing.

Although the SON leadframe 110 is shown having terminals for a firstchannel (a first Rx/driver die) and a second channel (a second Rx/driverdie), for single-channel applications there may be only a single thermalpad. However, a single Rx/driver die may not be able to support multiplechannels because the channel-channel voltage of >200V is too high. Thelead terminals of the SON leadframe 110, including a disclosed splitthermal pad comprising VSSA and the VSSB terminals with a Rx/driver dieon each thermal pad, enables meeting the high channel-channel voltagedifferences when a single Rx/driver die cannot meet this requirement.The half-etched lead terminals 115 may be referred to as being signalpads that support a Tx/signal coding die. The SON leadframe 110 cangenerally be used for all applications benefiting by the disclosedability to tailor the leadframe lead terminal spacing to supportdifferent levels of voltage differences. Alternate arrangements can setthe spacing between lead terminals including the thermal pads asappropriate for particular application requirements.

FIG. 1B is a top view depiction of a disclosed MCM package 160 using theSON leadframe 110 shown in FIG. 1A that now shows a Tx/signal coding dieshown as a Tx die 130 on the lead terminals on the input side of the MCMpackage 160. There is also a first and a second Rx/driver die shown asfirst Rx die 141 and second Rx die 142 on the lead terminals on theoutput side of the MCM package 160, as well as bond wire connections.Die-to-die bond wires are shown as 167, and bond wires from the Tx dieto any of the half-etched lead terminals are shown as 168 a, and thebond wires from any of the Rx die are shown as 168 b. The die-to-diebond wires 167 are generally spaced apart between 50 μm and 200 μm. Moregenerally, this spacing may be set to a specific profile to achievevoltage clearance within the MCM package, whereby the voltage potentialof the die-to-die bond wires 167 is separated by a sufficient spacing toavoid damage. A mold compound is shown as 157. The respective die 130,141, and 142 are shown mounted face up with a die attach materialunderneath (see FIG. 2 described below for example die attachmaterials).

On the input side, a portion of the Tx/signal coding die 130 sits abovea full-thickness portion of the half-etched lead terminals 115 of theSON leadframe 110 and a portion sits above a half-etched portion whichis unsupported by metal on its outer side, which is in contrast toconventional chip on lead designs where the die sits across from twoseparate leads which are fully supported by metal on either side. Thehalf-etched lead terminals 115 can be seen to be all parallel to oneanother, typical dimensions for the half-etched lead terminals 115 mayhave a 0.25 mm width, a total length of 1.2 mm, and half-etched lengthof at least half of the total length, such as being 0.7 mm. As describedabove, the Tx/signal coding die is generally attached using anon-conductive die attach material, such as a conventional epoxy.

FIG. 2 is a cross-sectional view of the MCM package 160 shown in FIG. 1Btaken across a width of the package, but not along a line, to show theVSSB terminal of second Rx die 142 and one of the half-etched leadterminals shown as 115 a that includes a full-thickness portion 115 a ₁and a half-etched portion 115 a ₂. The Tx die 130 is shown mounted inpart on the full-thickness portion 115 a ₁, and in another part on thehalf-etched portion 115 a ₂. The half-etched lead terminals have a widthand a total length that is generally at least four times the width.Moreover, to as described above help support a higher voltage differencebetween the input side of the MCM package and an output side of the MCMpackage, the length of the half-etched portion 115 a ₂ is generally atleast one half the total length.

A die-to-die bond wire 167 is shown. There is also a bond wire 168 ashown between a bond pad 131 a on the Tx die 130 a half-etched leadterminal 115 a, and a bond wire 168 b between a bond pad 161 on thesecond Rx die 142 and the VSSB terminal.

The second Rx die 142 and the Tx die 130 each comprise a substrate 105 aand 105 b, such as comprising silicon, including circuitry for each dieshown as 180 a and 180 b having nodes connected to bond pads 131 a and131 b, respectively. Circuitry as used herein comprises circuit elements(including transistors, and generally diodes, resistors, capacitors,etc.) formed in a semiconductor region that is configured together forgenerally realizing at least one circuit function.

The Tx die 130 is now shown with a B-stage die attach material 137 onhalf-etched lead terminal 115 a that includes a full-thickness portion115 a ₁ and distal half-etched portion 115 a ₂. A B-stage epoxy filmcomprises a partially cured versions of traditional epoxy resins.B-stage films can provide the same function as traditional heat-curingepoxies. B-stage films are processed by positioning at the bondinterface, and heating to complete the polymerization reaction and bond.B-stage films are typically provided as a film sheet or more often inprecut shapes and forms with release liners.

The Rx die 142 is now shown with an epoxy die attach material 143 on aterminal shown as the VSSB terminal. The Tx die 130 is shown by examplehaving an on-chip HV ISO device 230 in its signal path. However, the HVISO device 230 can also be on the Rx die 142 in the signal path, or onboth of these die.

FIG. 3 shows an example first assembly flow 300 for forming a disclosedMCM package, according to example aspect. Although not specificallydescribed, disclose assembly flows including first assembly flow 300generally utilize leadframes that are in a conventionalblock/array/panel so that many MCM packages can be processedconcurrently. Step 301 comprises obtaining a leadframe having leadterminals with half-etched features, such as shown as half-etched leadterminal 115 a including a full-thickness portion 115 a ₁ and ahalf-etched portion 115 a ₂ in FIG. 2 . Step 302 comprises applying adielectric die attach material shown as a B-stage die attach material(film) to the backside of a Tx/signal coder wafer. Alternatively, thedielectric die attach material may comprise a screen-printed dielectricmaterial. Step 303 comprises sawing a Tx/signal coder wafer to provide aplurality of singulated Tx/signal coder die. Step 304 comprisesplacement of a Tx/signal coder die top side up on the lead terminals onthe input side of a leadframe having half etched lead terminals.

Step 305 comprises sawing a Rx/driver wafer to provide a plurality ofsingulated Rx/driver die. Step 306 comprises applying a conductive dieattach material shown as an epoxy die attach material that generally hashaving metal particle filling (such as filled with silver particles) tothe lead terminals on the output side of the package including on theVSSA terminal and the VSSB terminal (thermal pads). The conductive dieattach material is defined herein as a material that provides a 2°5° C.thermal conductivity of at least 1 W/m·K. In contrast, conventionalnon-thermally conductive die attach materials generally have a 2°5° C.thermal conductivity of about 0.2 to 0.3 W/m·K. The conductive dieattach material can comprise a metal particle filled epoxy material, aceramic, a composite material, solder, or sintered nanoparticles.

Step 307 comprises placement of the Rx/driver die on the epoxy on thelead terminals on the output side of the leadframe. Step 308 comprisescuring of the B-stage die attach material and the epoxy die attachmaterial. Step 309 comprises wirebonding, including die-to-diewirebonding. Step 310 comprises molding and generally symbolizing.Symbolizing generally comprises using a laser to ablate the top surfaceof the package to “write” the part number, the lot code, and otheridentifying information.

Step 311 comprises package singulation. Disclosed methods includingfirst assembly flow 300 can further comprise applying a pre-tape on abottom side of the leadframe, and after forming the mold compoundremoving the pre-tape. The adding of the pre-tape on the bottom side ofthe leadframe provide additional mechanical stability. The pre-tape isgenerally removed after molding when the leadframe is more mechanicallystable due to the presence of the mold compound.

FIG. 4 shows an example second assembly flow 400 for forming a disclosedMCM package, according to an example aspect. Step 401 comprisesobtaining a leadframe having some half-etched features, such as shown inFIG. 2 . Step 402 comprises applying a B-stage die attach material tothe backside of a Tx/signal coder wafer. Step 403 comprises sawing aTx/signal coder wafer to provide a plurality of singulated Tx/signalcoder die. Step 404 comprises placement of a Tx/signal coder die on thehalf-etched leads. Step 405 comprises curing the B-stage die attachmaterial.

Step 406 comprises sawing a Rx/driver wafer to provide a plurality ofsingulated Rx/driver die. Step 407 comprises applying a conductive dieattach material shown as an epoxy die attach material that generally hashaving metal particle filling (such as filled with silver particles) tothe lead terminals on the output side of the package including on thethermal pads. Step 408 comprises placement of the Rx/driver die on theoutput side of the leadframe including on the thermal pads. Step 409comprises curing of the B-stage die attach material. Step 410 compriseswirebonding including die-to-die wirebonding. Step 411 comprises moldingand symbolizing. Step 412 comprises package singulation.

EXAMPLES

Disclosed aspects are further illustrated by the following specificExamples, which should not be construed as limiting the scope or contentof this Disclosure in any way.

FIG. 5 shows an example application for disclosed MCM packages as partof an isolated DC/DC telecom brick module 500 shown implemented on a PCB590, having DC/DC converter shown as a power converter 520 comprising aconverter input side 516 and a converter output side 526 on both sidesof a HV ISO device on the PCB 590, shown by example as a transformer 530a. There are two MCM packages shown in FIG. 5 as MCM package 160 acomprising Tx die 130 a and Rx die 141 a/ 142 a, and MCM package 160 bcomprising Tx die 130 b and Rx die 141 b/ 142 b. Each Rx die has areceiver with a gate driver that provides a gate driver output showncoupled to the respective gates of the transistors of the converterinput side 516. Having the two MCM packages 160 a and 160 b is generallyneeded to collectively drive the four transistors shown in the converterinput side 516, which is described in more detail below.

The isolated DC/DC telecom brick module 500 can be used as a 48V brickpower supply module for telecommunication systems, which generallyrequire HV isolation up to 2.25 kV DC, input-to-output creepage of atleast 1.3 mm, channel-to-channel isolation of at least 100 V, andenhanced cooling by providing low thermal impedance to enable operationunder high PCB 590 temperature or high ambient temperature. The PCB 590is shown having a PCB isolation barrier 592 (e.g., 1.3 mm wide) whichseparates the converter input side 516 and the converter output side526, where the PCB isolation barrier 592 is bridged by the transformer530 a, and by the MCM packages 160 a, 160 b. As described in more detailbelow, because the MCM packages 160 a, 160 b are electrically connectedto the converter input side 516 that can experience high voltage surgesor transients, for example during a surge/transient at about 1.5 kV, theMCM packages 160 a, 160 b both include the HV ISO device 230 shown inFIG. 2 . PE shown in FIG. 5 represents a protective earth groundreference.

The converter input side 516 (or primary side) is shown by exampleincluding four power MOS devices configured in a full-bridgeconfiguration powered by a battery 510. The converter output side 526 isshown comprising transistors and gate drivers shown as the dual low-sidegate driver 539 shown coupled for driving the respective gates of thetwo transistors on the converter output side 526, where the converteroutput side 526 may in this case also be called the secondary side. Asuitable DC/DC power converter 520 for use together with a disclosed MCMpackage for system modules such as the isolated DC/DC telecom brickmodule 500 shown, can be obtained commercially.

The 48V (nominal) voltage shown applied to the transistors on theconverter input side 516 is shown provided by a battery 510 that powersthe converter input side 516. The converter output side 526 which is ona side of the transformer 530 a opposite relative to the converter inputside 516 is shown having an output at 12V as an example, and is isolatedfrom voltage surges and transients which may occur on the converterinput side 516.

The converter output side 526 transistors and other components need tobe isolated from the converter input side 516, so that voltagedisturbances and transients (e.g., a surge from the 48V battery inputlines to PE) received at the converter input side 516 do not affect theconverter output side 526 and its connected circuitry. The transformer530 a on the PCB 590 (and the HV ISO device 230 in the MCMs) provide theHV isolation to realize the side-to-side isolation for the transientvoltages applied to the converter input side 516. The converter outputside 526 needs voltage regulation to meet the desired output voltage (inthis case the 12V level) at output 538 based on a varying input DCvoltage provided by the battery 510 on the converter input side 516 thatapplies its DC voltage across an input capacitor 512. The converterinput side 516 has an output coupled to one side (the primary side) ofthe transformer 530 a, where the other side of the transformer 530 a iscoupled to an input of the converter output side 526.

The microcontroller 535 is configured including connections to enablesensing the voltage level at the output 538 that is taken across anoutput capacitor 527 on the converter output side 526 in responsetransmitting information in the form of modulated data signals from theTx input to the Rx output of the MCM packages 160 a, 160 b from theconverter output side 526 to the converter input side 516. Themicrocontroller 535 thus provides a control signal to each Tx input thatcommands each Rx output to adjust the duty cycle or frequency of a gatedrive voltage applied to gates of the transistors on the converter inputside 516 to achieve the desired voltage regulation and best powerconversion efficiency. Since signals are transmitted from one side ofthe transformer 530 a (i.e., from the converter output side 526 to theconverter input side 516), the MCM packages 160 also needs a HV ISOdevice as shown in FIG. 2 . The microcontroller 535 is also showncoupled to control the dual low-side gate driver 539, where the duallow-side gate driver 539 controls the bias level applied to the gates ofthe transistors of the converter output side 526.

Since as described above the MCM packages 160 a and 160 b are alsooperating (electrically connected to) the nominal 48V converter inputside 516 controlling the high side and low side transistors configuredin a full bridge configuration, the MCM packages 160 a, 160 b also needto sufficient terminal-to-terminal spacing from HV terminals (e.g.,terminals that touch 48V such as the ground reference for the high-sidegate driver output of Rx die 141 b connected to the high-side transistorgate) to its low-voltage terminals (e.g., terminals operated at 10-12Vpotential such as the gate drive supply for the low-side gate driveroutput of Rx die 142 b connected to the low-side transistor gate.

The MCM packages 160 a, 160 b provide 1.2 mm spacing from one outputchannel (i.e., the high-side driver ground reference, for example, theoutput of 141 b) connected on the converter input side 516 to the otheroutput channel (i.e., the low-side gate drive supply for, for example,the output of 142 b) also connected on the converter input side 516. TheMCM packages 160 a, 160 b can generally meet the following three keyrequirements for use in modules including a DC/DC power converter, suchas the DC/DC power converter 520. These three requirements comprise:

-   1) voltage transient requirements and lead terminal spacing for    input-to-output terminal isolation (for example, 707V, 1.5 kV or    2.25 kVDC for is and 1.3 mm);-   2) High-voltage to low-voltage lead terminal spacing of at least 1    mm for the two channels, and-   3) thermal pads also called power pads for improved heat    dissipation.    Disclosed MCM packages are also 36% smaller in size as compared to    the commercially available MCM packages that are believed to only be    able to meet requirements 1) and 2).

Junction-to-air thermal resistance (θ_(JA)) is a measure of the abilityof a device to dissipate heat from the surfaces of the die to theambient through all possible paths. Experiments were performed todetermine the thermal performance of a MCM package 160 molded withplastic including a Tx/signal coding die, and a first and a secondRx/driver die on a disclosed leadless leadframe including first andsecond thermal pads. It was found that the inclusion of thermal padstypically reduced the θ_(JA) of the MCM package by about a factor oftwo, and the ψ_(JB) (junction-to-board thermal parameter) reduced byabout a factor of 6.

Disclosed aspects can be integrated into a variety of assembly flows toform a variety of different MCM packages and related products. Althoughnot shown, the MCM package can also comprise stacked IC die, besideslaterally positioned IC die. The IC die may include various elementstherein and/or layers thereon, including barrier layers, dielectriclayers, device structures, active elements and passive elementsincluding source regions, drain regions, bit lines, bases, emitters,collectors, conductive lines, conductive vias, etc. Moreover, the IC diecan be formed from a variety of processes including bipolar,insulated-gate bipolar transistor (IGBT), CMOS, BiCMOS, and MEMS.

Those skilled in the art to which this Disclosure relates willappreciate that many variations of disclosed aspects are possible withinthe scope of the claimed invention, and further additions, deletions,substitutions and modifications may be made to the above-describedaspects without departing from the scope of this Disclosure.

The invention claimed is:
 1. A multi-chip module (MCM) package,comprising: a leadless leadframe including a plurality of lead terminalsincluding a plurality of half-etched lead terminals that include afull-thickness portion and a distally located half-etched portion, andsecond lead terminals including at least one thermal pad; a first dieattached by a dielectric die attach material to the plurality ofhalf-etched lead terminals, the first die comprising first bond padscoupled to first circuitry including circuit elements configured forreceiving a control signal and for outputting a coded signal at aselected frequency, and a transmitter; at least one second die attachedto the second lead terminals, the second die comprising second bond padscoupled to second circuitry including circuit elements configured for areceiver with a gate driver, wherein the second die is attached by aconductive die attach material to the thermal pad; bond wires includingdie-to-die bond wires between a portion of the first bond pads and aportion of the second bond pads; at least one high-voltage isolationdevice between the transmitter and the receiver, and a mold compound forencapsulating the first die and the second die.
 2. The MCM package ofclaim 1, wherein the at least one second die comprises the second dieand a third die, wherein the at least one thermal pad comprises a firstthermal pad and a second thermal pad, and wherein the second die isattached to the first thermal pad and the third die is attached to thesecond thermal pad.
 3. The MCM package of claim 1, wherein the leadlessleadframe comprises a small outline no leads (SON) leadframe.
 4. The MCMpackage of claim 3, wherein the plurality of half-etched lead terminalsis on a first side of the MCM package, and wherein the second leadterminal portion is on a second side of the MCM package opposite thefirst side.
 5. The MCM package of claim 1, wherein the dielectric dieattach material comprises a film lamination, and wherein the conductivedie attach material provides a 2°5° C. thermal conductivity of at least1 W/m·K, and comprises a metal particle filled epoxy material, ceramic,a composite material, solder, or sintered nanoparticles.
 6. The MCMpackage of claim 1, wherein an external spacing between the half-etchedlead terminals and the thermal pad is at least one of at least 1 mm andat least 30% of a length of the MCM package.
 7. The MCM package of claim1, wherein the plurality of half-etched lead terminals is parallel toone another, and wherein some of an area of the first die is positionedabove the full-thickness portion and another area of the first die ispositioned above the half-etched portion.
 8. The MCM package of claim 1,wherein the plurality of half-etched lead terminals has a width, and atotal length that is at least four times the width, and wherein thehalf-etched portion is at least one half the total length.
 9. The MCMpackage of claim 1, wherein the high-voltage isolation device comprisesa high-voltage transformer or a high-voltage capacitor.
 10. A method ofassembling a multi-chip module (MCM) package, comprising: providing aleadless leadframe including a plurality of lead terminals including aplurality of half-etched lead terminals that include a full-thicknessportion and a distally located half-etched portion and second leadterminals including at least one thermal pad; attaching a first die witha dielectric die attach material to the plurality of half-etched leadterminals, the first die comprising first bond pads coupled to firstcircuitry including circuit elements configured for receiving a controlsignal and for outputting a coded signal at a selected frequency, and atransmitter; attaching at least a second die using a conductive dieattach material to the thermal pad, the second die comprising secondbond pads coupled to second circuitry including circuit elementsconfigured for a receiver with a gate driver; wherein there is at leastone high-voltage isolation device on the first die or on the second diebetween the transmitter and the receiver; positioning bond wiresincluding die-to-die bond wires between a portion of the first bond padsand a portion of the second bond pads, and forming a mold compound forencapsulating the first die and the second die.
 11. The method of claim10, a shared curing step is used for the attaching of the first die andthe attaching of the second die.
 12. The method of claim 10, where theattaching of the first die comprises a first curing step and theattaching of the second die comprises a separate second curing step. 13.The method of claim 10, wherein the die-to-die bonds wires are spacedbetween 50 μm and 200 μm.
 14. The method of claim 10, further comprisingapplying a pre-tape on a bottom of the leadless leadframe, furthercomprising after forming the mold compound removing the pre-tape. 15.The method of claim 10, wherein the at least one second die comprisesthe second die and a third die, wherein the at least one thermal padcomprises a first thermal pad and a second thermal pad, and wherein thesecond die is attached to the first thermal pad and the third die isattached to the second thermal pad.
 16. The method of claim 10, whereinthe dielectric die attach material comprises a film lamination, andherein the conductive die attach material comprises a metal particlefilled epoxy material, ceramic, a composite material, solder or sinterednanoparticles.
 17. The method of claim 10, wherein the plurality ofhalf-etched lead terminal is parallel to one another, and wherein someof an area of the first die is positioned above the full-thicknessportion and another area of the first die is positioned above thehalf-etched portion.
 18. The method of claim 10, wherein the pluralityof half-etched lead portions has a width, and a total length that is atleast four times the width, and wherein the half-etched portion is atleast one half the total length.
 19. A telecom module, comprising: aDC/DC power converter having a converter input side configured forreceiving a DC voltage that is applied to an input of a high-voltageisolation device that provides a DC output voltage to a converter outputside, at least one multi-chip module (MCM) package, comprising: aleadless leadframe including a plurality of lead terminals including onan input side a plurality of half-etched lead terminals that include afull-thickness portion and a distally located half-etched portion, andon an output side second lead terminals including at least one thermalpad having a pad area; a first die attached by a dielectric die attachmaterial to the plurality of half-etched lead terminals, the first diecomprising first bond pads coupled to first circuitry including circuitelements configured as a first receiver for receiving a first controlsignal and for outputting a coded signal at a selected frequency, and afirst transmitter, wherein there is a first on-chip high-voltageisolation device between the first receiver and the first transmitter;at least one second die attached to the second lead terminals includingthe thermal pad, the second die comprising second bond pads coupled tosecond circuitry including circuit elements configured as a secondreceiver for a receiver for receiving a second control signal, thereceiver with a gate driver, wherein there is a second on-chiphigh-voltage isolation device between the second receiver and the secondtransmitter, wherein the second die is attached by a conductive dieattach material to the thermal pad, and wherein an area of the seconddie is within the pad area; bond wires including bond wires between thefirst bond pads and the half-etched lead terminals, bond wires betweenthe second bond pads and the second lead terminals, and die-to-die bondwires between the first bond pads and the second bond pads; and a moldcompound for encapsulating the first die and the second die; acontroller coupled to the converter input side and to the converteroutput side, wherein the controller is configured to: sense a voltagelevel at an output of the converter output side, and transmit an ACcontrol signal to the converter output side that is transmitted acrossthe high-voltage isolation device to the converter input side to controla voltage applied to gates of transistors of the converter input side toachieve a desired voltage regulation and a higher power conversionefficiency.
 20. The telecom module of claim 19, wherein the telecommodule is assembled on a single printed circuit board (PCB) thatincludes the high-voltage isolation device, wherein the converter inputside comprises a full bridge converter, and wherein the at least one MCMpackage comprises a first MCM package and a second MCM package.